1. Ministry of Food, Agriculture and Fisheris Danish Institute of Agricultural Sciences Simulation of nitrate leaching from an organic dairy crop rotation with different manure types and loads J. Berntsen, J.E. Olesen, B.M. Petersen, J. Eriksen Danish Institute of Agricultural Sciences Introduction Management of nitrogen in dairy systems is especially difficult due to the use of organic manures and the residual effects of pastures. During grazing a considerable build-up of soil N is often observed. Ploughing of the grassland is therefore followed by a large mineralisation that might exceed the demand of the subsequent crop. This might lead to large amount of nitrate being leached. In addition, rotations dependent on organic manures rather than mineral fertilizers are believed to have a higher risk of nitrate leaching. Conclusions The FASSET model was able to capture the general trends in experimental data set. Effects of manure type and level on nitrate leaching were small and less than 10 kg-N ha -1. The scenarios showed that the nitrate leaching depends on soil type, climate and fertility. The range was from 39 kg-N ha -1 at the low fertility loamy sandy soil with a dry climate to 85 kg-N ha -1 at the high fertility sandy soil with a wet climate. References Berntsen, J.,Petersen, B. M., Jacobsen, B. H., Olesen, J. E., and Hutchings, N. J. 2003. Evaluating nitrogen taxation scenarios using the dynamic whole farm simulation model FASSET. Agricultural Systems 76: 817-839 Eriksen, J.,.Askegaard, M., and Kristensen, K. 1999. Nitrate leaching in an organic dairy/crop rotation as affected by organic manure type, livestoc density and crop. Soil Use and Management 15: 176-182 Petersen, B. M., Berntsen, J., Jensen, L. S., and Hansen,S. 2003. CN-SIM – a model for the turnover of soil organic matter. I Long term carbon and radiocarbon development. Soil Biology and Biochemistry (subm.) Both simulations and measurements indicate that the effects of the different types of organic input are small and the effect of the level of input is between 3-7 kg-N/ha. The crops had different leaching potential. Winter wheat had the highest simulated nitrate leaching followed by barley/pea mixture, oat, spring barley, beets and grass-clover. A similar crop ranking was observed in the measurements. Fig 1. Observed and simulated N-leaching in the HL treatment. Method A dairy crop rotation experiment was established at Foulum, Denmark in 1994 (Table 1 and Eriksen et al. 1999) with four treatments: high slurry (HS), low slurry (LS), high deep litter (HL) and low deep litter (LL). These levels correspond to livestock densities of 0.9 and 1.4 livestock units ha -1. The FASSET model (Berntsen et al., 2003) was used to simulate the above experiment. The model is a whole farm model that contains a crop-soil-atmosphere model, which simulates daily changes in crop growth, soil organic matter and transport of several solutes. The soil organic matter model is based on Petersen et al. (2003). The model simulated all the different treatments in the years 1993 to 2002 using observed management, measured manure application and composition, measured climate data and soil characteristics. Results Simulated and observed nitrate concentrations are shown in figure 1 for the HL treatment. There was a general good agreement between simulations and observations. Scenarios Based on the above crop rotation a set of scenarios was constructed focusing on the following effects: Soil type: sandy (Jyndevad) and loamy sand (Foulum) Climate: wet (Jyndevad) and dry (Tystofte) Soil Fertility: 3 and 1.5 %C in top soil. Archived at http://orgprints.org/00001700http://orgprints.org/00001700